1. The Field of the Invention
The present invention relates to systems and methods adapted for use in waste recycling and conversion. More specifically, the present invention relates to the recycling and conversion of solid waste derived, for example, from domestic and commercial refuse.
2. The Relevant Technology
Commercial, industrial, and residential consumers generate large amounts of throw-away and waste products (i.e., municipal solid waste) that need to be handled and disposed of in an environmentally satisfactory manner. Disposal of municipal solid waste (hereinafter “MSW”) has traditionally presented a number of problems.
MSW is typically disposed of by landfilling and/or incineration. The waste products in landfills are typically either raw garbage or incinerator ash. These methods of waste product disposed contaminate the soil, water and air. Environmental restrictions as well as land usage demands for housing have reduced the number of sites available for landfills.
Incineration (i.e., the mass burning of waste products) is rapidly becoming a non-viable alternative in heavily populated areas. Public outcry over the air pollution associated with burning garbage has halted nearly all new incinerator construction.
In response to these waste disposal problems, governments and the public have demanded that, wherever possible, recycling systems should be employed both to conserve material resources and to reduce pollution problems. Efforts have been made to recover valuable resources such as glass, plastic, paper, aluminum, and ferrous and non-ferrous metals from waste materials. For example, households in many cities are asked to sort their garbage into recyclables (e.g., paper, plastic containers, metal containers and glass containers) and non-recyclables. However, rates of non-compliance and mis-compliance are high. That is, some customers fail to sort their waste or they sort incorrectly, which either shunts recoverable materials into the waste stream or contaminates the recyclable stream with waste materials. Non-compliance and mis-compliance reduce the efficiency of and increase the costs associated with operating a recycling system that is designed to processed pre-sorted waste.
In contrast, some recycling systems attempt to dispense with the problems associated with pre-sorting by attempting to recover recyclable materials from mixed waste. However, many of these systems are fraught with the tendency to be highly labor intensive to operate, while offering relatively low recovery rates of recyclables. Furthermore, these types of recovery facilities or programs still do not recover much of the energy rich wet and dry organic materials, which are mostly landfilled as residue.
Many recycling systems configured to work with pre-sorted waste or mixed waste are designed to recover specific materials and/or form specific products. The components of these systems are arranged and designed to recover certain individual fractions such as combustible organic materials, aluminum, ferrous metals, glass, plastic, and miscellaneous bulky inorganic materials. Efficient resource recovery depends in large part upon separating the maximum amount of desirable material from the refuse using relatively few separating components and minimizing the percentage of unwanted materials in the individual fractions.
Nevertheless, the energy balance of many recycling systems is sub-par or, in some cases, negative. For example, many recycling systems tend to misdirect recoverable materials, which reduces the efficiency of downstream processes and wastes much of the valuable energy and/or materials that may otherwise have been recaptured from the recovered waste. In other cases, the processes of recovering, transporting, and recycling the recyclable materials are so inefficient that they consume more energy than could be saved by simply landfilling the garbage and making new products from raw materials.